An idiom is a a common manner of speaking in a certain language -- words and phrases which everyone can identify as carrying a specific meaning.
Idioms intrigue me. I found a site of common English idioms. www.idiomsite.com. Give it a look and see how many you recognize.
If you know idioms which are common to a certain region or state, I would love to hear them. For instance, the South has some great expressions of speech -- I will get to them next time. If you know a great idiom, leave me a comment. Aren't words wonderful?